1. Field of the Invention
The present invention relates to an optical molding process and an optical molding apparatus which mold a desired resin model by scanning and irradiating a photocurable resin such as an ultraviolet light curable resin by a light beam, and more particularly relates to an optical molding process and an optical molding apparatus which quickly returns the level of the liquid surface of the photocurable resin liquid contained in the photocurable resin liquid tank to a constant level so as to shorten the molding time and improve the molding precision.
2. Description of the Related Art
An attempt has been made, for example, to mold a desired resin model by scanning the surface of a tank containing an ultraviolet light curable resin liquid with an ultraviolet light laser, while turning it on and off, so as to cure the same and successively building up scanned and cured layers on an elevator. This resin model is used as a master model for other products, for example, so during molding it is necessary to improve the molding precision, the interlayer bonding, and the molding efficiency.
The conventional optical molding process, as shown in FIG. 1, involved generating an ultraviolet light beam 5 from an ultraviolet light laser 4, using an optical system having galvanomirrors and shutters etc. to turn the ultraviolet light laser on and off and control the scanning direction of the beam, and while doing so irradiate the surface of the tank 1 containing an ultraviolet light curable resin liquid 2. In the tank was provided an elevator 8 which blocked the ultraviolet light laser and could be made to ascend and descend. The resin liquid present between the surface 3 of the resin liquid and the elevator 8 was cured by the ultraviolet light laser beam 5.
In the first step of the molding process, the elevator 8 is made to ascend and the resin liquid 2 present between the resin liquid surface 3 and the elevator 8 is cured by the ultraviolet light laser beam 5 to form an n-th scanned and cured layer 7a, then the elevator 8 is made to descend and the same procedure as with the n-th layer is followed to form an (n+1)th scanned and cured layer 7b on the n-th scanned and cured layer 7a. The same procedure is followed so as to successively build up (hereinafter also referred to as "deposit") scanned and cured layers. When the final scanned and cured layer finishes being formed, the elevator 8 is made to ascend and the model 9 is taken out from the resin liquid, then final curing is performed by using an ultraviolet light lamp etc. to irradiate the entire model with ultraviolet light over a long period.
Below, in the present invention, planes at identical pitches of movement of the elevator are referred to as "constant-height sections". In one constant-height section, there will be regions for curing the resin liquid and regions for not curing the resin liquid in accordance with the three-dimensional shape of the desired model.
The ultraviolet light beam generated by the ultraviolet light laser oscillator is used for scanning along the scanning direction by the optical system. During scanning, in regions where the resin liquid is to be cured, the ultraviolet light laser is turned on (in actuality, the shutter AOM is opened) and in regions where the resin liquid is not to be cured, the ultraviolet light laser is turned off (in actuality, the shutter AOM is closed). When one scanning line finishes being scanned, the optical system is controlled to shift in phase by the amount of a scanning pitch and similar scanning is performed along the scanning direction once again.
Note that if an ultraviolet light beam is scanned into a resin liquid, the light energy is gradually reduced by the resin liquid, so microscopically speaking, sharp edged irradiated regions (that is, scanned and cured layers) are formed.
The scanned and cured layers of constant-height sections are formed in this way. In successively building up the scanned and cured layers, when forming a top scanned and cured layer, the beam intensity is made enough so that the ultraviolet light beam is irradiated to the bottom layer as well, that is, the depth of curing in the constant-height section is controlled to be greater than the built-up thickness, so as to improve the bonding between layers.
When molding the next scanned and cured layer after molding a scanned and cured layer at one constant-height section, as mentioned above, the elevator 8 is made to descend. However, the descent of the elevator is accompanied by an increase in the immersed volume of the elevator (mainly the support rods of the elevator), which causes photocurable resin liquid to overflow from the photocurable resin liquid tank. An overflow tank 13 is provided at the outside of the top edge 11 of one side of the photocurable resin liquid tank to receive the overflow.
To return the photocurable resin liquid 2 which overflowed at the time of the descent of the elevator once again to the photocurable resin liquid tank, provision is a recirculation pump 14 is provided between the photocurable resin liquid tank 1 and the overflow tank 13. Note that this recirculation pump has the function of agitating an anaerobic photocurable resin liquid in addition to that of returning the overflowed photocurable resin liquid to the photocurable resin liquid tank.
However, in a conventional optical molding apparatus, since the photocurable resin liquid is high in viscosity, when the elevator was made to descend, there was the problem of too much of an overflow. The narrower the gap between the elevator and the tank wall during the descent of the elevator, the faster the flow rate of the photocurable resin liquid passing through it and the more the photocurable resin liquid flowing out into the overflow tank.
In particular, to maintain the liquid surface constant, in actual operation, when the elevator was made to descend, the elevator was intentionally immersed to more than the thickness of the scanned and cured layer next to be molded, then was made to ascend to the normal position. This resulted in the problem that rippling of the liquid surface was aggravated and the amount of photocurable resin liquid which overflowed increased as well.
This problem becomes more conspicuous the closer the elevator is to the liquid surface.
If the light beam scans with a low liquid surface in this way, since it is taught that the control of the optical system requires first that the liquid surface be at its normal position, the precision of the molded model will be damaged. Therefore, in the past, scanning was delayed until the liquid surface rose due to the photocurable resin liquid returned by the recirculation pump and after it was confirmed that the liquid surface had risen to its normal position, the next scanned and cured layer was molded. Accordingly, there was waste in the molding time. Improvement in molding time is provided by the present invention.
If the amount of the flow of the recirculation pump is increased, the liquid surface of the photocurable resin liquid tank could be quickly restored. However, if this measure is employed, there are the problems that rippling on the liquid surface becomes greater that requires time to settle down. Also, by increasing the amount of liquid returned to the photocurable resin liquid tank, the liquid surface rises above its normal position.
The present invention was made in consideration of these problems in the prior art and has as its object quickly returning the position of the liquid surface of the photocurable resin liquid stored in the photocurable resin liquid tank to a constant position so as to shorten the molding time and improve the molding precision.